Transiently regenerative amplifiers with response controlling means



11g 2, 1966 P. LEFFERTS TRANSIENTLY REGENERATIVE AMPLIFIERS WITH RESPONSE CONTROLLING MEANS Filed Jan. 24. 1964 6 Sheets-Sheet 1 lUlU E m m XE@ m m M WQN J T. F M RSV 2Q m m m n@ .W n.@ m R w SQ H v m. E@ NNRH n m QQ .b M .v SQ hn F NQS w l0 G EN E@ M New m y QW @N QQ SN Rw K/j QQ, ...l M a@ 5 l@ Ns@ RQ NN@ n QN m Sm QQ`W` mmm w m n 5% .am N@ 595m ...ma Q ww@ SQ 5W asm NQNQ m fQQmN L QON ATTORNEYS Aug. 2, 1966 P. LEFFERTS 3,264,5'3

TRANSIENTLY REGENERATIVE AMPLIFIERS WITH RESPONSE CONTROLLING MEANS Filed Jan. 24, 1964 6 Sheets-Sheet 2 INVENTOR.

PETER LEFFERTS MORGAN, FINNEGAN,DURHAM 8a PINE ATTORNEYS Aug. 2, 1966 P. LEFFERTS 3,264,573 TRANSIENTLY REGENERATIVE AMPLIFIERS WITH RESPONSE CONTROLLING MEANS rxled Jan 24. 1964 6 Sheets-Sheet 3 @35 jl KZ' D25 n i R 38 F luGrBB @www Flfac Fla-3D0 Vm V www] n m n V FIGrBF L-LMULLILJLFLJU ,NVENTOR PETER LEFFERTS BY MORGAN, FINNEGAN,DURHAM 8| P\NE ATTORNEYS Aug. 2, 1966 P. LEFFERTs 3,264,573

TRANSIENTLY REGENERATIVE AMPLIFIERS WITH Filed Jan 24. 1964 RESPONSE CONTROLLING MEANS 6 Sheets-Sheet 4 BY MORGAN, FINNEGAN, DURHAM 8x PINE ATTORNEYS Aug. 2, 1966 P. LEFFERTS 3,264,573

TRANSIENTLY REGENERATIVE AMPLIFIERS WITH RESPONSE CNTROLLING MEANS ATTORNEYS Aug. 2, 1966 P. LEFFERTS TRANSIENTLY REGENERATIVE AMPLIFIERS WITH RESPONSE GONTROLLING MEANS 6 Sheets-Sheet 6 Filed Jan. 24. 1964 INVENTOR PETER LEFFERTs MORGAN, FINNEGAN, DURHAM a. PINE wud.-

ATTORNEYS United States Patent O 3,264 573 TRANSIENTLY REGENRATHVE AMPLHFIERS WITH RESPONSE CONTROLLING MEANS Peter Leiferts, Princeton, NJ., assignor, by mesne assignments to TIA Electric Company, Laurence Township,

NJ., a corporation of New Jersey Filed lian. 24, 1964, Ser. No. 340,066 31 Claims. (Cl. S30-26) This application is a continuation in part of applicants prior copending application, Serial Number 258,811 now abandoned, for Transiently Regenerative Ampli-fiers With Response Controlling Means, filed February l5, 1963 and assigned to the assignee of the instant application. Related subject matter is also found in applicants prior copending application, Serial Number 258,735 for Transiently Regenerative Amplification, filed February l5, 1963 and also assigned to the assignee of the instant application.

This invention relates to feedback circuits employed with electronic devices and more particularly to stored feedback circuits employed with transiently regenerative amplifiers.

Transiently regenerative amplifiers such as those disclosed in applicants above-noted copending application, Serial Number 25 8,735, may be employed in a variety of applications including those calling for a switched output in response to an extremely low-level input signal. These regenerative amplifiers are subject to a regeneration control wherein the regenerative function is alternately activated and disabled independently of the input signal, and at a rate high with respect to the input signal frequency. During the periods of activated regeneration, the input signal is incrementally sensed whereby the amplifier output attains one of two regenerated states according to the polarity of the input signal.

The transiently regenerative amplifier is extremely sensitive and for many applications it is desirable to reduce this high gain momentarily and at desired intervals. Such a modification of the response of the transiently regenerative amplifier has many uses such as limiting the effects of noise and spurious transients, and stabilizing the operation of the amplifier.

In addition, it is often desirable to bias the input circuit of a transiently regenerative amplifier in a desired direction and over a period of time with respect to the last regeneration of said amplifier to impart characteristics thereto giving rise to various modes of operation such as periodic cycling. l

Thus, it is possible to control the response or the characteristics of a transiently regenerative amplifier by means of time-varied reference levels supplied to the input circuit from feedback circuits, the feedback being stored, delayed and phasedA with respect to the input signal according to the requisites of the application.

The in-phase stored feedback circuits may be adapted to impart characteristics such as input sensitivity limitation and switching stability.

The out-of-phase stored feedback circuits may impart characteristics such as cycling, linear operation and cancellation or reduction of latching tendencies.

Accordingly, it is an object of this invention to provide flexible and economical means for controlling the characteristics of a transiently regenerative amplifier thereby adapting sai-d amplifier to a multiplicity of varied applications.

Another object of this invention is to provide means for varying the gain of a transiently regenerative amplifier over a selected period of time by means that transiently bias the input circuit.

Another object of this invention is to provide simple and fiexible time-controllable and amplitude-controllable ICC feedback means for controlling the input circuit of a transiently regenerative amplifier, so as to produce desired response characteristics.

A still further object of the invention is to provide feedback control means in transiently regenerative ampli- 'fiers for achieving phase sensitivity.

Another object of this invention is to limit the sensitivity of a transiently regenerative amplifier over a selected period of time thus reducing the effects of noise and spurious transients.

Another object of this invention is to provide means for biasing the input circuit in aiding relationship to the preceding input signal thereby imparting a latching characteristic to the transiently regenerative amplifier.

Yet another object of this invention is to provide delayed feedback means opposing a latching bias so as to override said bias at a determinable instant in time whereby the transiently regenerative amplifier is restored to full sensitivity. v

Another object of this invention is to provide means for producing a switching duty cycle Within a transiently regenerative ampli-fier which is variably controllable by the input signal.

An additional object of the invention is to provide means for providing a linear response characteristic in transiently regenerative amplifiers.

Another object of this invention is to provide means for generating a variable duty cycle output of a transiently regenerative amplifier suitable for conversion to a linear output.

A still further object of the invention is to provide in transiently regenerative amplifiers means for combining positive and negative feedback signals in various proportions and according to various time relationships to inipart desired response characteristics thereto.

These and other objects and advantages of the invention will be set `forth in part hereinafter and in part will be obvious herefrom, or may be learned by practice with the invention, the same being realized and attained by means of the instrumentalities, combinations and improvements pointed out in the appended claims.

IFIGURE 1 is a schematic diagram of a transiently regenerative amplifier employing in-phase stored feedback;

FIG-URE 2 is a schematic diagram of a transiently regenerative amplifier employing in-phase stored feedback adapted for use With a differential input.

FIGURE 3 is a schematic diagram of a transiently regenerative -amplifier and diagrammatic responses thereof, employing both in-phase stored feedback and out-of-phase stored feedback;

FIGURE 4 is a schematic diagram of a transiently regenerative amplifier employing in-phase stored feedback and out-of-phase stored feedback and including temperature sensitive means and preamplier means;

FIGURE 5 is a schematic diagram of a transiently regenerative amplifier employing out-of-phase feedback for effecting linearized operation; and

FIGURE l6 is a schematic diagram of a transiently regenerative amplifier employing an in-phase feedback circuit for effecting phase sensitivity.

FIGURE l illustrates a circuit disclosed in FIGURE 9 of the applicants aforementioned copending application, Serial Number 258,735, 4differing by the addition herein of the elements and connections shown in bold outline. The circuit connections and operation common to both applications are described below.

The circuit shown to the left of the terminals 201 through 205 illustrates external connections and resistances which are arranged and adjusted according to the intended application. In the illustrated embodiment the resistors 300, 301 and 302 have been interconnected with 3 the terminals 201, 202, 203 and 205 in order to provide sensitive relay type operation.

Terminals 201 and 202 constitute the input terminals. Terminals 203 and 205 conveniently provide reference potentials `derived from a reference supply (Ref. Supply) included in the unit to impart versatility thereto and facilitate a wide variety of applications. The voltage at teru minal 203 is adjustable while the voltage at terminal 205 is fixed. Input power is supplied at terminals 207 and 208, being fed from the available power source. The output circuit comprises a relay K100 and associated contacts, the latter opening and closing according to the amplitude of the input signal.

The reference supply comprises a full wave rectifier including a secondary winding SW91 of a transformer T100 and, -diodes D91 and D92. The transformer is energized by way of primary winding P90.

Connected across the output terminals of the rectifier in the reference supply is the series combination of a resistor R90 an-d a pi filter comprising C90, R91 and C91. Connected across the output of the pi filter is a divider R02 and R03. The latter is adjustable and has the potential developed at its arm coupled to terminal 203 via resistor R91. The negative side of the reference supply is connected to terminal 205. The voltages appearing at terminals 203 and 205 comprise substantially constant D.C. potentials which are regulated and stabilized by a circuit connected across the divider R02, R90. This circuit includes a transistor Q90 interconnected with another transistor Q91.

One branch of the regulating circuit comprises a series combination of resistor R95, the emitter-collector of Q90, and a Zener diode D93. A second branch comprises resistor R90, the collector-emitter of Q91 and a resistor R90. The base of Q90 is connected to the junction of R97 and the collector of Q91. The base of Q91 is connected to the junction of the collector of Q90 and the Zener diode D90. The foregoing arrangement serves to provide `a stabilized potential across resistor R90l and hence yields stabilized potentials at the terminals 203 and 204. Thus it may be seen that the potential across D tends to be 1 constant whereby the collector current of Q91 tends also to be constant. The stages Q90 and Q91 interact to produce a constant current through the Zener diode D03 to stabilize the aforementioned reference potentials.

The input section of the sensing circuit includes R100 connected across input terminals 201 and 202. In serial relationship across R100 is the series combination of resistor R101 and parallel, oppositely-polarized diodes D102 and D103. Connected in shunt with the diodes is a capacitor C100. filter and to prevent damage to the sensing circuit through malfunctions or errors associated with the input circuit. Thus the diodes D102 and D103 prevent the developmentof excessive base-emitter potential inthe sensing circuit.

From the input section, the sensed signal is coupled `to the base of input stage Q100 and to the intermediate point of a divider R102 and R103 via a coaxial line M100. The sensing circuit including the divider is connected across the source comprising secondary winding SW100 and diodes D100 and D101 in full wave configuration. This source produces a pulsating potential which is applied to terminals E100 and E101 of the sensing circuit. As noted hereinafter this potential provides the intermittentlyactivated regeneration described generally hereinbefore and in greater detail hereinafter.

The collector of Q100 is connected to E100 via R101 while nected to theV base of the second stage, Q101. This base is also returned to the input connection at divider R102 and R109 by way of the parallel combination R109 and C101. The latter is designed to decouple transients from This input circuit is designed as a noiseV volves the connection of the collector of Q100 to theV base of `Q101 via the dividerwhich includesl R100,. R101 and R100. The common emitter connections to R105 provides the other-coupling.. When the potential B10043101 is low, the circuit is in a low gain state nothwithstanding its regenerative characteristic; there is therefore negligible response to the signal applied at terminals. 201 .and 202. When the voltage E rises however, the circuit is transformed to its high 4gain regenerative .and sensitivev state. During this intervalthe input'signal is sensed and produces a related `output at the collector of Q101.

The stages Q102 and Q103 are driven bythe collector output of stage Q101. The function of these rlatter two stages is to provide poweramplificationwhichthereby enables sensing stages Q100,V and Q101 to operatev at a relatively low and -constant power level. This arrangement mitigates toa .great iextent the temperature compensation problems arising from self-heating.

The base of Q102 is connected directly to the collector of Q101. The emitter of Q102 is connectedito E100 via R111. The collector of Q102 connects to E101 via thefseries combination R112 and R112. TheY junction :of these .two yisV connected to the baseoffQ103.

The emitter of `output stage Q103 is returned to E101 via R115. The collector is connected to VE100 via the out- Y put relay K100.

The circuit connectionwhich includes R114 introduces a regenerative characteristic in thepower amplifying stages Q102, Q102 toenhance theirinetgain.

In the illustrated sensitive ,relay application and;with

the input connections as shownresistor R99 is set to provide a voltage of desired value, say, 0.9 volt at terminal 203. A fraction of this reference voltagedetermined by the values of divider` resistorR302 and R300, is applied at input terminal 202.

tivel to ground).

It will be vassumedinitially thattthe input 'at-terminal 201 is less than 9'millivolts.' Under thesecondi-tions a negative signal voltage is applied to the base. of Q100.

During thehighly regenerative periods,l thisvoltage isl sensed and tends to reduce conduction of Q100. The collector voltage thus rises and :the potential across R105 due to Q100 falls, tending `thereby to increase conduction of Q101. The 1regenerative characteristicy accentuates this response and Q101 is 'driven to saturation.;

Under these conditions, the relatively` large. :potential across R lprovides large forward drive to Q102 whereby conduction of the ,latter increases. The resultant increased potential across R113 serves toy increase forward.

creased .beyond the threshold value. i The actionV is cycli-Y cally repeated so long as-` the. input at terminal 201 remams less. than 9 millivolts. yDiode D101 across VK100 keeps the latter energized nothwithstanding the repetitive action, until the input signal changes to a value effective.-

to cause switching.

This has the beneficial effect of eliminatingV The source of this regeneration lies in they Illustratively, this adjusted ref-'f erence voltage may be of theV value `9 Inillivoltsy (posiy If the input should change to a value greater than 9 millivolts during the next regeneration period Q100 is turned full on and Q101 is full off. Thus stages Q102 and Q103 are cut off and relay K100 de-energized. The normally-open contacts close to complete any desired output circuit such as the energizing circuit of a control device or indicator. The normally-closed contacts are opened and may perform related tasks such as disabling, transfer and other functions. This switching is effected with a very small change in input, say from 9 millivolts to 10 millivolts. Using a convenient commercial relay, e.g., an Elgin Advance type MV-120D- 31, load currents of 2 amperes per contact set are switched in response to this small input signal. In eX- ample, power gains of the order of 1013 are readily obtained. So sensitive is the circuit that care must be exercised in contending with noise and other spurious conditions.

In order to mitigate this problem in applications where the full response characteristic is not required, there is provided in the illustrated amplifier means for limiting circuit sensitivity during certain intervals and under certain conditions. As embodied these means take the form of a feedback T network interconnecting the base of Q101 and the collector of Q102 and shown .in bold outline. Thus, the series branch of the T comprises R120 conected to the base of Q101 and R121 connected to the collector of Q102. The shunt element comprises capacitance C120 connected to source point E101.

The function of the sensitivity control means is to impart a memory function to the overall circuit. A type of limited hysteresis results; thel control means store a voltage on C120 related to the previous signal input which effected an output response (switching of K100). This voltage is in aiding relationship with succeeding signal inputs of the same relative polarity and tends to remain as a charge on C120 for a period equal to at least several sensing cycles. This charge on C120 is attenuated by the divider comprising R120 and R109 and, thus reduced, is applied to the base of Q101 in aiding relationship to successive signals of the same general amplitude condition. Noise and other spurious inputs so far as they tend to switch the circuit out of its las-t state, are thus opposed. On the other hand, a sustained and definite change in the signal to -be sensed overcomes this offset-ting effect and .provides a new response.

With the foregoing arrangement, effective and controllable limitations on the sensitivity of the overall circuit are provided during certain conditions and intervals thereby limiting the effects of noise and other spurious actions without substantially impairing basic circuit response.

The amplitude of the feedback supplied to the base of Q101 may be varied by changing the resistance of R120. A higher resistance of R120 reduces the amplitude of the feedback, and conversely a lower resistance of R120 increases the feedback amplitude.

An input signal changing its polarity must achieve a sufiicient level at the base of Q101 to override the latching feedback amplitude at that point `before the combined effective potential there follows the polarity of the changed input. Thus, the regenerative amplifier will continue to switch into a certain state, although the input signal has changed polarity, until the level of the changed polarity signal equals and cancels the stored feedback amplitude, thus causing an effective null input condition. It is to be understood that such a null exists for each of the two possible switched states of the regenerative amplifier, defining between them the range of input signals insufficient to switch the regenerative amplifier into its opposite state. 1

Outside the nulls, the polarity of the input signa predominates over the feedback level and determines the state of amplifier switching.

A very small feedback signal, corresponding to a high 6 resistance of R120, results in a very small band of insensitivity between the two nulls.

If R is made to be adjustable as by a potentiometer, the band of insensitivity may be varied thereby to suit requirements of operation. Adjustment of the desensitized band may be made to compensate for varying amounts of spurious signals and noise in the input signal. By employing two paralleled feedback circuits, each such as the one shown in heavy lines in FIGURE 1 and each with an oppositely-poled diode in series for polarity discrimination, the amount of feedback may be made to differ in amplitude between each of the two switching polarities, That is, a relatively small signal may be made sufficient to switch the amplifier in one direction, while a selectively larger signal may be required to switch the amplifier back again.

Various additional applications are made possible by the feedback circuit. For example, the circuit of FIG- URE l may be used as a signal threshold indicator. Signals of a new polarity below the threshold set by the feedback amplitude fail to switch the amplifier, while signals above this threshold operate to switch it.

A relatively short time-constant is desired for the feedback circuit when used as a sensitivity-limiting arrangement. Capacitor C120 should be small enough in this application to delay the feedback only slightly, so as to bias the amplifier input at the required level by the time of the next succeeding regenerative cycle from the power supply.

The use of a large time constant, obtained by changing the value of C120 to a larger capacity, results in transient regenerative amplification having altered characteristics. If the time constant is fairly long relative to the regeneration control frequency, the feedback inuence is negligible for a time after an amplifier switching action. The amplifier is thus still highly sensitive and a random input signal will cause switching as if no desensitizing feedback were provided. However, upon the sustained occurrence of a signal having a particular polarity, the feedback has an opportunity to build up in amplitude. Thus, as time goes on, an increasingly stronger input signal of the opposite polarity is required to switch the amplifier. In effect, the amplifier acquires a habit of switching into the particular state sustained for a time by an input signal. After a sufficient time to acquire a habit, the occurrence of a very large input signal of opposite polarity will switch the amplifier to its opposite state, but the previously acquired habit will tend to be retained. If the large amplitude of the new input decreases immediately, the amplifier will go ba-ck to switching into its prior state in accordance with the habit acquired in the feedback circuit. Thus a sustained input signal having a new polarity is required to break the habit.

A variation of the habit circuit described above is one employing a fast acting (short time constant) feedback circuit in combination with a long-time constant, slow acting, feedback circuit. In this arrangement only one large signal of new polarity is required to break the habit, as the fast feedback circuit output would cancel the habit retained by the long time-constant circuit. Potentiometers used in the feedback circuits could vary the habit-acquiring and habit-breaking characteristics of `the circuit.

Referring to FIGURE 2, the circuit therein employs a transiently regenerative amplifier together with stored feedback means in aiding relationship with the input signal. The -circuit of FIGURE 2 is thus similar in these respects to `the circuit of FIGURE 1.

The circuit of FIGURE 2 is illustratively used as a sunshine-sensing device, having a dual photocell input and a recorder output. This circuit comprises a power supply; an input circuit and signal preamplifier comprising transistors Q1 and Q2 with associated circuitry; a transiently regenerative amplifier comprising transistors Q3 and Q4 with associated Icircuitry; a stored feedback circuit F' comprising resistors R13, R19 and capacitor C1; and an output indicating circuit including a recording device `\l.

Photocells PC1-PC2 provide a differential input to the preamplifier whose output is employed to switch the transiently regenerative amplifier according to light relations sensed by-PC1 and PC2. The stored feedback circuit F latches the circuit in the appropriate switched state. When the regenerative amplifier output is of the state which operates relay K1, the contacts of the latter actuate solenoid K2 for controlling pen recorder N.

The power supply comprises full-Wave rectier transformer T1, together with diodes D2 and D3. Rectified A,C. from the tap on T1 is connected .through R14 to negative terminal B1 and directly from the connected cathodes of D2, D3 to positive terminal B2. Capacitor C2 is illustratively 0.1 microfarad, a value substantially less than that required for conventional filtering; it is used to decouple high frequency disturbances including noise. Thus lthe power output at B1-B2 is a pulsating D.C., returning to substantially zero potential every halfcycle.

The input to the preamplifier is illustratively from photoelectric cells PC1 and PC2. Photocell PC1 is conveniently located` in a shaded outside area so as to continually register the light intensity of shade. Photocell PC2 is conveniently disposed to receive sunlight or a derivative thereofso as to register the light intensity therefrom. Photocells PC1 and PC2 may be conveniently arranged in a weather-protected device, PC1 being shaded by a ring suitably disposet to the suns ecliptic. In the absence of sunlight, both photoelectric cells register `relatively similar light intensities. When the sun appears, PC2 indicates the sunlight intensity, registering a greater output than PC1 which indicates the shadow intensity level at that time.

The two photocells are connected .differentially to the preamplifier comprising stages Q1 and Q2. The photocell common connections are connected via input terminal C to the arm of balance potentiometer R3. The PC1 signal lead is lconnected via terminal I1 to the base of transistor Q1; the PC2 signal lead is connected via I2 to the base of transistor Q2.

Potentiometer R5 is connected between the bases ofV Q1 and Q2; its arm, besides connection to the photocell common connections noted above, is returned to the junction of serial resistances R1 and R9 in a divider across B1, B2 which comprises serial elements R1, R3 and diode D1. Potentiometer R3 is adjusted to balance the photocell outputs so that a condition of relatively similar lightY intensity at the cells results in relatively equal signals at the bases of Q1 and Q2.

The emitters of Q1 and Q2 are tied together and connected through R13 to power terminal B1. The collectors of Q1 and Q2 are connected to the bases of Q3 and Q4 respectively and thence via circuits in the regenerative amplifier as described more fully hereinafter to power terminal B2.

The transiently regenerative amplifier comprising Q3 l The bases of Q3 R5 to obtain the balance between transistors Q3 and Q4 1 required for proper initiation of regeneration.

The collectors of Q3 and Q1-are each returned through a respective resistance R12 and R13 to negative supply 8 Y. terminal B1. Resistor R1 completes the regenerative loop from the collector of Q4 to t-he base of'Q3,

The ditferentialinput signa'lfrom the photocellsl varies thecollector currents through transistors Q1 and Q2. A part of the collector current of transistor Q1 owsthrough the'base-emitter circuit of transistor Q3; similarly, part of the collector current of transistor Q2 ows through the base-emitter circuit of Q4.

As the pulsating supply bringszthe circuit components to conditions of operability, the collector current of transistors Q3 and Q4 increase. Depending on-the polarity of thephotocellfinput signal, the1current through one of theregenerative amplifier stages will be greater than the other. Assuming the signal at the base of Q1 to be more positive than that at the base of Q2, a greater current will ow through the collector'of Q1, and through the ybase-emitter circuit of Q3; as a consequence greater collector currentA will owthrough transistor` Q3. The collector currents through Q2 and through Q4 will be of correspondingly lesser value.

The increase in collector current through transistor Q3,

flowing through resistor- R3 to the momentarily positive supply,causes an increasedpotentialdrop across R3. Accordingly, the Q3V-Q4 emitters become more negative and the emitter of Q4 is thus made more negative with respect to its base potential. As a consequence, baseemitter current throughtransistor Q4 decreases, and the Q4fcollector current owing through R13 decreases.l As a result, the ,potential dropE across R13 decreases, and the negative-going potential at the collector of Q4 is transferred through resistor R1 back to the base of transistor Q3. This signal, transferred through resistor R7, aids the initial increase in base-emitter currentthrough Q3. Transistor4 Q3 thereforeincreases further in collector current conduction, in .turn causing fthe collector current through transistor Q4 to decrease further. The signal thus regenerates continuously untiltransistor Q3 saturatesV and transistor Q4is cut of.l At this time the output of the transiently regenerative amplifier, taken from the collector of transistor Q3, is at a maximum positive s value owing `to the saturating collector current of Q3 owing through resistor R12.

The maximum positive output of the regenerative arn-` plifier is coupled through resistor R13 to the base of relay transistor Q3. It may `be seen that the drop ,across the Q3f-collector 4resistor R12 is in parallel. with the divider R13-R11, the potential across R17 being applied to `the base-emitter circuit of Q5.

An increase in Q5 base-emitter. current, resulting from Y the positive output ofv Q3, causesin turn an increased collector-emitter currentthroughQ5. Thiscurrent flows through theeld ofrelay K1, energizing it, and causing, in the illustrated case, the contacts thereof to close. These contacts actuate an output device,.such as a solenoid K2 which is energized romfasourceB3. The solenoid K2 illustratively operates a pen P on a graphfGR,having a continuously moving recording medium driven by motor M. Thus, with motor -M continuously driving the recordGR, the pen `P will producefa mark onGR of a length related to the period of time in which the amplifier is in the ON state. This may conveniently correspond with periodsfofsunshine so that the occurrencel and length of same areKV indicated.

The signalat the base .of transistorQ5 also provides a source of feedback to be supplied to the base of pream-` plifier transistor Q1 in-an aiding relationship with the input signal from the photocells. This in-phase feedback is coupled through network F comprising R13, R13, and C1, to the lbase of Q1, capacitor- C1 affording a short timedelay.. The unctionof the components of the'feedback network is to delay'the feedback slightly and :als'o to attenuate it to a level. suitable for employment with the inputs fromthe photocells. Capacitor C1 chargesover a relatively short time interval toward the potential at the base of Q5, and ther feedback thereupon appears at the base of Q1 accordingly, very shortly after switching of transistors Q3 and Q4. The feedback remains at the base of transistor Q1 over several cycles of operation, aiding the potential of the photocell signal which originated the regeneration causing the relay output. So long 'as this feedback remains, small signals, noise, or interference which would otherwise tend to switch the regenerative amplifier into the opposite state will have no effect. In effect, the stored and delayed feedback described herein desensitizes the preamplifier input and influences the circuit to retain the regenerative switching condition of the signal which initiated the feedback. This effect is similar to that of FIGURE 1 and may be termed latching in View of the tendency of the in-phase feedback as described to maintain the same switching condition originated by a particular differential input signal until that input signal changes polarity and has, in addition, sufficient amplitude to overcome the b ias supplied by the feedback network to the input cir-cuit. When the latter occurs, the regenerative amplifier switches into the alternate state, `and the in-phase feedback consequent therefrom tends to maintain the s'aid alternate state. Thus latching occurs in both switched states.

In the illustrated case, the effect of the alternate switched state to the one rst described is to maintain deenergization of relay K1, thus maintaining deactivation of the pen solenoid K2. When Q3 is cut off and Q4 saturated, the Q3 collector output to the lb-ase of Q5 is negative, preventing the flow of emitter current through Q5 and the relay armature of K1.

The divider which is connected between B1 and B2 and which comprises R1, R3 and diode D1 serves several functions. The preamplifier is biased therefrom by a connection of the -arm of potentiometer R3 to the junction of R1 and R9. Diode D1 serves to compensate for temperature variations, varying the bias on the preamplifier according to the ambient temperature. Diode D1 also serves a biasing function in the early part of the regenerative cycle, owing to Iits non-linear characteristic at the lower portion of its conduction curve. As the A.C. cycle commences, power is applied sinusoidal-ly and operating potentials are applied across the transiently regenerative amplifier and the preamplifier. The bias potential applied at the arm of potentiometer R6 is at first a relatively large proportion of the divider voltage owing to the initial high impedance of D1 at that early part of the A.C. cycle. Thus the base potentials of Q1 and Q2 rise quickly. Subsequently, at a certain point in the A.C. cycle the impedance of diode D1 decreases, tending to thereafter maintain the preamplifier bias at a suitable level determined by the drop across R3 and D1 in series.

FIGURE 3A illustrates a transiently regenerative ampliiier employing stored feedback in-phase with the input sign-al. This in-phase feedback circuit is similar in operation to the feedback circuit of FIGURES 1 and 2. In addition, a stored out-of-phase feedback circuit is employed.

The circuit of FIGURE 3A comprises a power supply, a transiently regenerative amplifier comprising Q21 and Q22 with associated circuitry, and output switching circuit comprising Q23 Iand Q24 with associated circuitry, an inphase feedback network R33, R34, and C21, and an out-ofphase feedback network R31, R32 and C22.

The input signal at terminals E21-E22 is supplied directly to the Q21-Q22 regenerative amplifier. Transient activation |and disabling of Q21-Q22 is furnished by the power supply. The output of Q22 is inverted by Q23 and supplied to relay-actuating transistor Q24, which controls output relay K21. The in-phase stored feedback circuit provides latching in a manner similar to that described in connection with the circuits of FIGURES 1 and 2. The out-of-phase stored feedback circuit provides latching cancellation, and, for applications in which `the out-of-phase feedback amplitude is designed to exceed the in-phase feedback level, a duty cycling function is obtained in a manner to be described hereinafter.

The periodic disabling and actuation of Q21-Q22 is controlled by the pulsating D.C. voltage at terminals 'V-l, V- of unfiltered full-wave power supply T21, D21 and D22. The cathodes of D21 and D22 are tied together and provide the pulsating positive voltage at V+. The center tap of the T21 secondary is the negative, or common return, at V-.

An input signal, illustratively in the low millivolt range, is impressed at terminals E21-E22 across input transistor R21. Input terminal E21 is connected directly to the base of Q21, and input terminal E22 is connected to the junction of a power supply voltage divider R22, R23 and therefrom through R27 to the base of transistor Q22. In effect, this arrangement provides a differential conection of the input signal to Q21-Q22 and any unbalance therein will act to switch the amplifier into the appropriate regenerative state.

The :amplifier circuit includes common emitter resistance R24 which is returned to power terminal V-, and respective collector resistances R25, R26 which are connected to V-l. The collector of Q21 also connects to a series branch comprising R23, potentiometer R22 and R30, the latter connects to V-. The arm of potentiometer R23 is connected to the base of O22, being adjusted for amplifier balance so that equal currents liow in each circuit; this insures that equal and opposite minimal detectable input sigals will regenerate Q21 and Q22 in the appropriate direction during the periodic -application of the power supply potential at V-|-, V-.

Assuming a more negative input at E21, at the application of power at V+, V- less base-emitter current flows through Q21 than through Q22. As a result, collector current through Q21 is lower and the potential at the collector thereof is higher. This increased potential is copuled through resistor R23 and through part of potentiometer R29 to the base `of transistor Q22. As a result of the increased potential at the base of transistor Q22, increased collector current flows therein. The increased collector current through Q22 is the result of the input signal being amplified by both Q21 and Q22; therefore, the increase in Q22 collector current is greater than the decrease in Q21 collector current caused by the negative input signal at E21. The net current flow through common emitter resistor R24 is therefore increased, and the result is a more positive potential at the emitters of Q21 and Q22. This positive potential reduces further the base-emitter current through Q21, causing the Q21 collector current to further decrease. This action continues regeneratively until Q22 is saturated in the fully-on conductive state, and Q21 is cut off.

The output of the transiently regenerative amplifier is conveniently taken from the collector of Q22 and supplied to the base of transistor Q23. Under the assumed input condition (base of Q21 relatively negative), transistor Q22 is full on, its collector is more negative as is the base of Q23; increased Q23 base-emitter current thus flows. Consequently increased collector current flows in Q23 and through R36 and R37 in the collector return. The resulting potential at the junction of R31,` and R311, which is connected to the base of Q24, increases. This results in increased base-emitter current through relay transistor Q24, causing the Q24 collector current to increase. As the increased collector current flows through the relay K21, it is energized, closing the normallyopen contacts; this action constitutes the output switching which is seen to be consequent upon a negative-going input at E21. If E21 were positive, Q22 is cut `off by regeneration and the relay K21 is `de-energized.

The increased collector-emitter current of Q24 flowing through R39 causes a more positive potential to appear across R33; this potential is coupled through R33 back to the emitter of Q23 reinforcing the increased collector current therethrough. This positive feedback function serves to insure a corresponding positive relay actuation.

The in-phase stored feedback network R34, R33 and C21 in T configuration functions as follows. For .the assumed input condition, the positive-going potential at the collector of transistor Q23 is coupled through feedback resistor R34, delayed slightly and stored by the relatively small capacity of storage capacitor C21. The voltage on C21 is coupled through the relatively high resistance of R33 back to the base of transistor Q22. The positive-going direction of this feedback is in-phase with the input signal at B21-E22 which illustratively caused the base of transistor Q22 to originally become ymore positive during the transient regeneration which followed circuit activation by the rising power supply voltage. Inasmuch as the feedback is delayed slightly, it has no effect upon the initial regenerative action which produces the feedback.

The in-phase delayed feedback as stored by capacitor C21, lasts over at least one cycle of power supply pulsation. Thus, the in-phase feedback provides a latching effect, Vi.e., a tendency for the transiently regenerative amplifier to ,unbalance into the original switched state whenever the power supply permits regeneration. An input signal of changed polarity and of sufficient amplitude to cancel this latching tendency is required before switching to the alternate state will occur.

This latching tendency operates in conjunction with an opposing and ultimately dominating tendency furnished by the out-of-pha-se feedback network R31, R32, and C22. The out-of-phase feedback is taken from the collector of Q22, which is more negative under the assumed input condition at E21wE22. This more negative potential is coupled through feedback resistor R31, delayed appreciably by the relatively large capacity of storage capacitor C22, and further coupled by feedback resistor R32 back to the base of transistor Q22. The values of the components of the feedback circuits are for this application selected to produce a greater delay in the out-of-phase feedback than in the in-phasefeedback. In addition, the values may be also selected to yield an out-of-phase peak feedback level exceeding the peak level of the in-phase feedback for obtaining the oscillatory duty cycle action described below.

The in-phase stored feedback is quickly impressed upon the transiently regenerative amplifier at the base of Q22, acting to latch the regenerative amplifier, and in effect decreasing the sensitivity of the amplifier so that only a new input exceeding the in-phase feedback level can accomplish amplifier switching. The in-phase feedback is quickly established at a level which illustratively lasts over a number of regeneration cycles. Then, several power cycles later, the out-of-phase delayed feedback begins to exert an appreciable effect, gradually rising in potential and thus increasingly opposing the in-phase feedback.

The out-of-phase feedback continues to increase, completely cancelling out the effective latching derived from the in-phase feedback, and producing a resultant .preponderance of out-of-phase feedback at the base Iof transistor Q22. Should this occur with a relatively small signal input, the amplifier will regenerate during the next enabling cycle in a direction opposite its prior state. If a larger input signal exists, the out-of-phase feedback has to cancel out the combination of input level and positive feedback signal before switching into the alternate state will occur. The greater the input signal, the longer-it takes for :the delayed out-of-phase feedback to achieve the necessary cancellation level. Hence, it can bey seen that the period during which the outputswitching is in the ,direction dictated by the input signal, i.e., is repetitively switching into the preferred state, is related to the amplitude of the input signal.

`where the assumed input signal again predominates.

'the switched state.

Once the negative feedback signalbecomes dominant over the. positive feedbackand theY assumed input-at E21, transistor Q21 is switched full on an-d transistor Q22 is cut olf. The output of the transiently regenerative amplifier is then .most positive, cutting off transistor Q23 and thus cuting Ioff relay transistor Q24. In this state ofthe regenerative amplifier, relay K1 is not energized.,

The reversal-in -output switching `causes a coresponding polarity reversal in the iii-phase stored feedback whereby the latter is now additivefwith the long time constant negative feedback and in opposition to the lassumed input. A succession of output pulses in the non-preferred direction thus occurs. However, the .negative feedback now gradually reverses polarity until the condition is reached It can be seen that this will occur. more or .les-s rapidly in dependence on the amplitude of the kinput si-gnaL When the transition occurs, the input signalswitches the regenerative amplifier back `to its original 4preferred state where K1 is energized.

The cycling of the Iregenerative amplifier continues in .this manner unless affected -by changesin Vthe input signal. A'sufficiently strong input signalfcan override the effect of bothrstored ,feedbacksr and maintain thev amplifier switch-ing in the preferredV state. This'is particularly advantageous :in control applications'where a large vinput signal reflects a system need for fullcont-rol action.

Lesser input signals affect the Aperiods of time kbetween the amplifiers preferred periods .and opposite periods. Thus, the periodsof a train yolf relay actuation pulses (eg. pulses, FIGS. 3B-3E) and a tra-in of relay deactivation pulses pulses, FIGS. 3C-3F) vary inversely to oney another .and are each affected by the magnitude and direction of the input signal. Hence,-the total effective time that output relay.K`21 is energized can1be made to vary from all the time (FIG. 3B)1to no: time (FIG.,3F), the transition lbetwen thesek extremes being smooth and continual and the proportion, of off time to on time being responsive to slight changes in the input signal level. Thus FIGS. 3C, 3D land 3E represent thefresponse to three input conditions comprising a negative input at E21 (FIG.13C), no input (FIG..3D) and a positive inputl (FIG-13E). Note that with no signal input at E21, the amplifier is in ybalanced oscillation, an-d equal periods of time are spent inteither state producing; equal periods of relay actuation Vand deactivation.

Resistor R38 is provided to insure relay actuation only during-those times when VQ22 is saturated, but not at times of amplifier balance or at times Q21y is saturated. Whenever current levels determined by .the .intermediate potentials of amplifier balance occur,-resistor R33 operates to regenerate the ,output circuit into a dre-'energized state.

Diode D23 by-passes the induction pulse produced by the relay K21, preventing this pulse from affecting the circuit.

An alternate application of the circuit of FIGURE 3 may be `obtained by'varying the stored feedback characteristics. In the proportioned control just described, the

maximum negative feedback exceeded maximum'positive i feedback. If,l however, the components of the. stored feedback circuits are changed to make. the peak amplitudes of the out-of-phase feedback `slightly less or equal to the peak amplitude of in-phase feedback, as by vincreasing the value .of R32 appropriately, a different mode of openation is obtained, wherein the amplifier periodically has increased sensitivity over the circuits of FIGURES 1 and 2 owing to cancellation of the latching feedback.l

Assuming the stored feedbacks are equal, and that the". relative time delays remain the-same as described above in ,connection with the circuit shown Yin FIGURE V3, inlphase feedback is applied immediately after a regeneration switching of the amplifier. As above, the presence of-in-ph-ase feedback at the base of transistor Q22 effectively desensitizes the input and latches the amplifier in Again, las abo-ve, at the moment of 13 latching and for some time thereafter, a new signal at the input of the amplifie-r of an new polarity must overcome the latching potential of the iti-phase feedback before the amplifier can be switched.

The out-of-phase feedback is delay longer than the imphase feedback, and builds up over many power supply cycles. As the out-of-phase feedback builds up, it increasingly opposes and cancels the effect of the in-phase feedback `at the base of transistor Q22. As the vout-ofphase feedback level approaches that of the in-phase feedback level, .the ilatching effect :is cancelled out. Eventual- 1y, the effective latching becomes so small as to be negligible, and the amplifier is then in a state of maximum sensitivity ready to regenerate according to the polarity ofv an input signal wpon the next application of power supply potential.

It should be noted that in order to obtain 'the latching cancellation and periodic maximum |gain just described, it is necessary that the stored out-of-phase feedback not exceed the level of the in-phase feedback at any time. Lf the out-of-phase feedback did exceed 'the in-phase feedback, the circuit would oscil-late in a manner similar to that above described in connection with proportioned control.

To facilitate the obtaining of a characteristic of periodic maximum gain with the circuit of FIGURE 3, R32 may be made adjustable. In the alternative, a mixing circuit may be emlployed in conjunction with the in-phase and out-of-phase stored feedback circuits to vary the ratio tof their outputs over a region near unity ria-tio. The optimu-m .gain 'condition is achieved when adjustment is made for unity ratio of feedback signals at their maximum amplitude. With this adjustment, the out-ofphase feedback eventually reaches a level cancelling out the latching effect of the in-phase feedback. At this time the input behaves as if no feedback of any kind existed, and .the maximum high gain of -the transiently regenerative amplifier is obtained. Precise 'adjustment is required for maximum gain, as the circuit would cycle were the out-o-phase feedback excessive, and insensitivity would remain to the extent the in-phase feedback were predominant.

Still further response varia-tions may be achieved by varying not only the relative levels, but the effective time constants of the feedback circuits as well.

It should be noted that the addition of voltage limiting means such as Zener diodes -at suitable points in the feedback circuit, e.g., across the storage capacitors, will eliminate the timing uncertainty normally inherent in an RC circuit.

Where the in-phase and out-of-phase networks provide long time constant and short time constant characteristics respectively, system response will depend on signal amplitude and on the direction of change of input signal magnitude.

Considering as a first condition, an input signal which is less than the relatively fast acting negative feedback, then each time the input causes switching to the preferred state, there is a following cycle in which the negative feedback predominates and causes switching to the opposite state. This oscillatory mode during signal null conditions is not infiuenced by the slow acting positive feedback voltage because the oscillation causes this voltage to average to zero and at most vary at low amplitude around its reference value. The oscillatory mode will persist so long as the input signal level remains below the effective negative feedback level. Hence for null signals, the oscillatory band is equal in magnitude to twice the effective level of negative feedback.

In a second condition where the applied signal exceeds the negative feedback level, the latter can not interfere with the usual switching to the preferred state. Moreover, the preferred switching is gradually reinforced with a latching tendency supplied by the slowly increasing positive feedback. Hence, once outside the null zone, for a few cycles the zone in effect appears to diminish. It will decrease to an extent dependent upon the ratio of the positive and negative feedback levels. If they are equal, the null zone appears to have vanished so far as transient short time departures of the signal are concerned. Thus a noise spike which transiently reduces the net input close to zero will not initiate the oscillatory mode because there is still an excess of combined signal and positive feedback which exceeds negative feedback. To return to the oscillatory mode, a change in input signal is necessary of a nature to overcome the stored positive feedback. In the illustrated case with the positive and negative levels equal, the signal must equal or cross zero. When this occurs oscillation commences. Hence the described arrangement is effective as a null detector, or, particularly where the positive feedback level exceeds the degenerative level, as a zero crossing indicator. By adjusting the ratio of positive and negative feedback, an oscillatory condition can be made to signify the reaching of a desired monitored or refe-rence level.

In more general terms the response characteristic has the frequently desired virtue of a Well defined, adjustable and stable null zone for signals within the null zone and -a stable, latched characteristic loutside the null zone.

It is thus seen that varying the relative levels of the stored feedback imparts different modes of operation to the transiently regenerative amplifier such as latching, cancellation or proportional control. Similarly, varying the delays of the stored feedback signals alters characteristics of operation such as the period of cycling or desensitized time. These may be calculated or determined for any given set of delays.

The circuit of FIGURE 4 shows a transiently regenerative amplifier having a temperature sensing input and employing both in-phase and out-of-phase stored feedback. In this respect, the circuit is most similar to the circuit of FIGURE 3. The circuit of FIGURE 4 is illustratively employed for controlling temperature by means of its switched output, which proportions the two output states according to the sensing of temperature deviation at its input.

The circuit of FIGURE 4 includes a power supply having several D.C. outputs, a temperature-sensitive bridge input circuit with a preamplifier, a transiently regenerative amplifier employing a gain chopping circuit to achieve periodic regeneration, an output switch amplifier, land inphase and out-of-phase feedback networks. The out-ofphase feedback network is illustratively designed to provide the greater effect whereby duty cycling or proportional control is provided such as described hereinbefore and illust-rated in FIGS. 3B-3F.

The positive potential for the line E+ is provided by diodes D45, D46 and D47 connected to the secondary winding of transformer T11 in combination with a filter network including R41, R42, C43 and C44. The negative potential for the line designated E is similarly supplied via diodes D43, D44 and D48 connected to the transformer secondary, and a filter network including R44, R45, C48 and C46. Diodes D41 and D42 in combination with a filter circuit including R40, C41 and C42 provide a positive potential to the collector of transistor Q48. The center tap of the T11 secondary winding is connected to ground.

The input to the circuit of FIGURE 4 is provided by temperature sensing means embodied as a thermistor N44 located in the device whose temperature is to be controlled. This thermistor constitutes one section of a bridge network which is balanced for zero output at the correct temperature. A deviation in temperature causes a bridge unbalance and the resultant output is amplified by preamplifier Q42-Q43 and used to switch transiently regenerative amplifier Q44-Q45 into the state corresponding to the direction of bridge unbalance.

The potential supplied across the temperature-sensitive bridge network is regulated by a Zener diode D49 which is in series with a resistor R70 across the negative D.C.

supply potential, conveniently `-20 v. D.C. The action of diode D40 reduces the effects of A C. components in the negative supply.

ground potential to the regulated negative potential present at the junction of D45 and resistor R70. One legconsists of resistors R74 and R75 in series, with the base `of preamplifier transistor Q45 connected to the junction thereof. The other leg comprises thermistor N41, which -is connected between ground and the base of Q42, and resist-ors R71 and R72 in series with N41 and connected between the base of Q42 and the negative potential at Vthe Zener diode anode.

The emitters of the bridge preamplifier transistors Q42 and Q43 are connected together and returned to the -20 v. D.C. negative supply potential through common emitter resistor R75. The collectors of Q42 and Q45 supply output currents to the base-emitter circuits of regenerative amplifier Q44-Q45.

The temperature-sensitive bridge is adjusted by means of potentiometer R72 for balance at the desiredtemperature affecting thermistor N41. A deviation from the desired temperature changes the resistance of thermistor N41 from -the balance value, and the bridge becomes unbalanced. The potentials at the respective bases of the preamplifier transistorsQ42 and Q45 are then no longer t equal with respect to their emitters, and t-he collector current in one transistor will begreater than -that of the other. Accordingly -t-he output of thepreamplifier is unbalanced `and greater ibase-emitter current will flow in the appropriate regenerative amplifier transistor. For example, if the thermistor resistance decreases, the potential drop across the thermistor similarly -decreases and the base of transistor Q42 becomes less negative or in other Words more positive. As `a result, increased base-emitter current fiows through Q42, thus also an increased collector `current fiows through Q42. This increase in Q42 collec-tor cur-rent flows through resistances R55 and R54 to the positive supply potential point E+ causing the base of transistor Q44 to become more negative. Less base-emitter current -iiows through transistor Q44 as a consequence. Similarly, the uri-balance in the preamplifier bridge resulting from Ia decrease in thermistor resistance .will cause a lesser collector current to flow through transistor Q45, a-nd a greater base-emitter current consequent-ly through transistor Q45. As noted more fully hereinafter, the activation of the regenerative amplifier Q44, Q45 is effected Iby the ungrounding of the .arm of `a potentiometer R55. The regenerative amplifie-r will then regenerate into the condition in which transistor Q45 is fully saturated a-nd Q44 is cut off.

The .inputs to transiently regenerative .amplifier Q44-Q45 are supplied via direct connection from the collectors of Q42 and Q45, respectively. The emitters of transistors Q44 and Q45.y are connected together and returned via R52 -to the negative D.C. operating potential at E-. The collectors of Q44 and Q45 are returned through respective serial resistance b-ranches .R55, R50 .and R55, R57 to E+. A clamp transistor Q45 parallels R57 in the Q45 collector return. The bases of Q44 and'Q45 are returned through resista-nces R55 and R57 respectively to a biasing point at the intermediate junction of voltage divider R54, R55 con- -nected between E+ and E-. T-he base of Q45 is also returned through resistance R51 to the arm of potentiomete-r R55 which is in the divider comprising serial elements R55, R54, R55 and R55 between E+ v. D.C. and E. Potentiometer R55 is adjusted for quiescent operating current balance between Q44 and Q45.

Regenerative amplifier Q44-Q45 includes regeneration control means for controlling periodic regenerationV therein. It may be remembered that in the case of the embodiments -of FIGURES 1, 2 and 3 unfiltered power supply potential provided such means. In the case of- The temperature-sensitive Vbridge is in parallel with vD45 and comprises two legs froml the circuit of FIGURE 4, the power supply is filtered. The enabling and disabling functions are furnished by ,a separateV chopper circuit which operates Yat the desired enabling frequency and which periodically jinterrupts the regenerative feedback circuit of Q44-Q45 thereby disabling it. A new regenerative period occurs each'time therinterruption ceases.

The regeneration control circuit includes diodes D43 and D44 which yprovide full-wave rectification of the A.C. power at the secondary of transformer T11. The `output is taken from the junction of their anodes, and is a pulsating D.C., negative with respect to the grounded center tap of the T11 secondary.

This pulsating D.C.`is Vapplied across a resistor R45, which along with serial resistances R45 and R45 comprise a divider between ,E+ and E- (unfiltered). The resultant potential appearing at the junction of R45 and R45 includes the negative-going pulsating signall of R45 and the positive reference level at fthe junction. This signal is connected to the base of asynchronizing transistor Q41 having a grounded emitter. Therefore, at times between half-cycles of the T11 output, thetbaseof Q41 becomes slightly positive with respect to its emitter, providing a reverse bias for cutting off collector current through Q41.

While transistor Q41 is` cut off, the cathode of rdiode D50 is consequently held negative with respect to ground by the voltage divider comprising R45, R50 and R47, connected-between E+ and E-.` The cathode of :D50 is connected to the junction of R451and R50` and being en-L ergized when Q41 is cut off; it permits current flow in the base-emitter circuit of chopper transistor Q45. This baseemitter current is sufficient to cause current .fiowin the emitter-collector circuit from ground into the emitter of Q45 to the arm of potentiometer R55,reducing the poten-'1 tial drop between the arm and ground to a llow value. Thus the arm is effectively grounded. This effective grounding ,interruptsv the regenerative feedback loop of amplifier Q44-Q45, which loop lincludes the pathl embracing the Ycollector of Q44, Idiode D51,R54, part of R55, thefbase-emitter of Q45 and-the base-emitter of Q44. By effectively .grounding theY arm of R55, regeneration-'cannot take place in Q44-Q45, and the circuit istthus disabled.

When `the negative pulse yapplied to R45 begins its cycle,

the-junctionzof R45, R45 becomes more negative; when this point drops below ground the base of Q41 is driven negative with respectto its grounded emitter'. Current then starts to flow in the base-emitter circuit thereof,`

causing collector current to flow throughk Q41; this action places the collector at approximately the same potential as the grounded emitter.v The collector is connected to the junction of R50 and R47; R50 andV R45 in series therewith lare thus placed between effective ground and E+..A Therefore, ther junction of R50 and R45, Vt-o which the lcathode of D50 is connected, becomes positive relative to ground.

Current thus cannot owthrough D50 since its anode is held at the lowerpotential occuring at the .mid-pointiof.

divider R51-R52 Awhich is` connected across the E+, E- supply. When no current iows through1D50 a positive potential results at the base of Q45 cutting off collector current fiowtherein. Thus Q45 becomes a high impedance and no-longer loads the regenerative feedback'floopA Attthat time, regeneration, is free to com- .mence therein. The polarity ofthe net input signal from the temperature-sensitive bridge preamplifier Q42-Q45 determines the regenerated state.

The operation of transiently regenerative amplifier Q44- Q45 is as follows: At the time transistor Q45 is cut off,l

the arm of potentiometer R55 is effectively ungrounded, and the regenerative Ifeedback circuit of Q44- Q45 is free to operate. Depending upon theunbaltance of theV signals supplied from theV collectors of preamplifier Q42-Q45, the resultant potentials at respectiveV bases of Q44-Q45 are similarly junequal. If the bridge is positive 17 at the base of Q42, greater collector current flows through Q42, R55, and R54 to E-lthereby making the `base of Q44, connected to the collector of Q42, more negative than the base of Q45. Reduced base-emitter current through Q44 is the result, and a lesser collector current flows in the Q44 emitter-collector circuit comprising R52 as a common emitter return for Q44 and Q45, .and R55 and R55 connected vfrom the Q44 collector to E+. Diode D51 and resistance R55 lare -in series, shunting R55-R55. This decrease in Q44 collector current causes the collector to become mo-re positive, and the potential is coupled from the collector of Q44 through D51 to the junction of R55 and R54 in divider R55, R54, R55, and R55 connected between E-jand E-. The positive-going potential at the junction of R55, R54 causes the potential at the arm of R55 to become relatively more positive; the larm potential is coupled through R51 to the base of Q45. An increase in Q45 base-emitter current results along with a consequent increase in emittercollector current. This emitter-collector current increase is amplified by Q45, and thus is greater in magnitude than the Q44 emitter current decrease earlier mentioned. 'llhe emitter currents of Q44 and Q45 both flow through R52, and the preponderance of the Q45 increase causes the common emitters to become more positive. The emitter-collector current through Q44 consequently decreases still further than the reduction originated by the bridge preamplifier unbalanc'e signal. That further collector current decrease through Q44 causes its collector to become more positive, which potential is .again coupled through D51, R54, R55, and R51 back to the base of Q45, causing a further increase in base-emitter and emitter-collecto-r current through Q45.

This action continues to circulate about the regenerative loop described until Q44 is cut off and the Q45 collector current is saturated. This particular regenerated condition occurs given an increased current output from preamplifier transistor Q42. If instead, the Q42 output current decreased, regeneration of Q44-Q45 would occur in the opposite direction, resulting in a saturation of Q44 and a cut-olf Iof Q45. The output of transiently regenerative amplifier Q44-Q45 is taken from the junction of R55 and R57, clamp transistor Q45 being in shunt with R57, in the Q45 collector return to E+.

The emitter of clamp transistor Q45 is connected to E-jand the base of Q45 is connected to the junction of R55 and R55 in series relation with the collector of Q44. When no Q44 collector current flows, the potential drop a-cross R55 is minimal, making the base of clamp Q45 approximately the same potential as its emitter. Under that condition clamp transistor Q45 is a high impedance, -and the Q45 collector current flow-s to a greater extent through R57 in parallel with the Ibase-'emitter circuit of switch transistor Q47. This Q45 current turns Q47 on, allowing maximum collector current to flow therein.

During the other two possible conditions of amplifier Q44-Q45, namely the condition of current balance between regenerative enabling, and the condition where Q44 is in saturation and Q45 is cut off, appreciable collector current from Q44 flows through R55, forwardly biasing Q46- When current flows in the 'base-emitter circuit of clamp Q45 it becomes a low impedance, and the Q45 collector is effectively placed at the same potential as its emitter, i.e., E+. The base of switch transistor Q47, connected to the collector of Q45, is thus yalso at E+. Since lche Q47 emitter is connected to E+, no base-emitter current flows through Q47 at this time, and Q47 collector current is cut off.

In this manner, when the regenerative amplifier Q44- Q45 is either transiently balanced or when transistor Q44 is regeneratively saturated, switch transistor Q47 is cut off. Only in the Iregenerative state of the amlpifier wherein transistor Q45 is saturated is transistor Q47 conducting.

The collector of Q47 is connected to the base of output switch transistor Q45. rPhe collector of switch transistor Q45 is conveniently returned to a positive D.C.

supply potential one or two volts higher than the E-lpotential at the emitter of transistor Q47. Thus when switch transistor Q47 conducts collector current, the base of output switch transistor Q45, directly connected to the collector of Q47, becomes more positive, being effectively at E+. In this condition, base-emitter current flows through Q45, allowing the emitter-collector circuit of Q45 to conduct heavily to the lhigher voltage bus. An output circuit is connected to the Q45 emitter circuit via a resistance R55, the other output terminal being ground.

Hence, when Q45 conducts, energizing current is delivered to the output circuit. This energizing output current thus flows only `at times amplifier tran-sistor Q45 is regeneratively saturated, and lat all other times is at a minimum.

Two feedback networks are provided, -an iti-phase feedback network comprising resistors R55 and R51 together with capacitor C45 is connected between the collector of switch transistor Q47 and the base of preamplifier transistor Q42; an out-of-phase feedback network comprising resistors R and R75 together with capacitor C47 is connected from the same point, the collect-or of Q47, to the base of pre-amplifier transistor Q45.

In this circuit the `infphase feedback functions similarly to the in-p'hase feedback of the circuit depicted in FIGURES l, 2 and 3. Capacitor C45 has a relatively small storage value, thus providing only a slight delay in the application of the in-phase signal. Similarly, as in the circuit of FIGURE 3, -resistor R51 is of relatively large value thus significantly attenuating this slightly delayed in-phase feedback. The result is a latching type of feedback which is impressed upon the preamplifier circuit immediately after the regenerative switching to provide a tendency to regenerate the circuit into the same switched condition upon the next enabling cycle from the chopper circuit.

The out-of-phase feedback circuit, as in the circuit of FIGURE 3, employs a relatively large storage capacitor, thus delaying this feedback appreciably. Resistor R75 is approximately a third of the resistance of the analogous resistor R51 in the indphase circuit. Thus the delayed outof-phase feedback level is attenuated less, appreciably eX- ceeding that of the in-phase level.

In a manner similar to that described in connection with the circuit of FIGURE 3, the delayed out-of-phase feedback increases over several enabling cycles and eventually reaches a level that cancels the in-phase feedback. The now predominating out-of-phase feedback network then impresses a resultant signal upon the preamplifier of a polarity opposite to the input signal polarity which originally switched the amplifier into its most recent train of regenerated states. When this new resultant signal occurs, the next enabling cycle causes the amplifier to switch into its alternate state.

In this manner, and as depicted in FIGURES 3A-3F, the regenerative amplifier produces a train of regenerated states of one condition, then, when the out-of-phase feedback exceeds the combination of the in-phase feedback and the input signal (assuming an input small enough to be overcome) the regenerative amplifier switches into its alternate state and produces a new train of similarly regenerated states of opposite polarity which continue until switching back again occurs. When the out-of-phase delayed feedback goes in one direction it -must oppose and cancel the in-phase signal plus the input signal; in the other direction, cancellation of the in-phase signal minus the input signal is required. In other words, the input signal aids the out-of-phase feedback in one direction and opposes it in the other. As a consequence, the outof-phase feedback cancels the combination more quickly when the input aids it, thus causing production of shorter train of regenerated pulses of one state. Similarly, 4the out-of-phase feedback takes longer to cancel the combination when the input opposes it, thus causing production of a longer train of pulses of the alternate state.

It should be noted that the output of FIGURE 4 comprises a train of pulses which in addition to being synchronizedwith the A.C. source frequency is also substantially in phase therewith. The pulses thus serve particularly well as control pulses for :load-controlling switch devices connected to the A.C. source since the switching of these latter devices will occur during low voltage intervals whereby transients and dissipation are reduced.

Referring tothe schematic of FIGURE 5, there is shown therein a transiently regenerative amplifier employing out-of-phase stored feedback to achieve certain linear response characteristics. The circuit includes a power supply, a transiently regenerative amplifier, a stored out-of-phase feedback circuit, an integrating circuit, and, in block form, a second transiently regenerative amplifier such as shown in FIGURE 1.

The power supply comprises T201 with a center tap forming terminal'V- and diodes D201 and D202 having their cathodes connected to terminal V+. 'Pulsating D.C. potential to the transiently regenerative amplifier Q201- Q202 is provided by the power supply.

The transiently regenerative amplifier comprising transistors Q201 and Q202 functions in a manner similar to those amplifiers described in connection with the circuits of FIGURES l, 2 and 3. That is, the pulsating D.C. potential supplied from the power supply at V+ and V- activates the transiently regenerative amplifier each half cycle.

Signal input terminal E201 is grounded, and terminal E202 is connected directly to the base of amplifier transistor Q201. The base of amplifier transistor Q202 is returned to ground through the parallel combination of R200 and C201. The signal ground point is connected to the midpoint of a divider R201, R202 connected between V+ and V+.

A positive potential at the input base of transistor Q201 results in increased base-emitter current through Q201, and consequently increased collector current through Q201, throughcommon emitter resistor R200, and through collector resistor R204.r The resulting negative-going potential from thecollector of Q201 is coupled through R200 and potentiometer R201 to the base of Q202. A regenerative action such as hereinbefore described thereby occurs with transistor Q201 becoming saturated in a fullon condition and transistor Q202 being cut off.

Conversely, a negative potential at the base of transistor Q201 will initiate regeneration of Q201-Q202 into the opposite state, wherein Q201 is cut off and Q202 is saturated full-on.

One end of potentiometer R207 is connected through R200 to V-, thus providing a range of adjustment about ground potential for balancing Q201 and Q202.

The output of the transiently regenerative amplifier is coupled'from the collector of Q202, through R211 and isolating diode D202 to feedback storage capacitor C202; the out-of-phase feedback is coupled from C202 through R213 back to the base of transistor Q202. This delayed outof-phase feedback causes the transiently regenerative amplifier to periodically produce output pulses of polarity opposite to that initially produced by the input signal.

Eac'h enabling pulse from the power supply places the transiently regenerative amplifier into a switching state determined by Ithe cooperation of the input signal at the base circuits of Q201 and Q202 with the out-of-phase feedback signal supplied from capacitor C202 through resistor R213 t the base circuits. The resultant preferred state is determined by the polarity of the input signal until such time as the delayed out-of-phase feedback level cancels out the opposing input signal level, thus becoming the preponderant signal input to the amplifier.r At -that time, the next enabling pulse'from the power supply will resul't in saturationof the amplifier in its nonpreferred, opposite state, producing a minority pulse output.

Switching into the minority state initiates the beginning;

of a corresponding delayed feedback having a tendency to aid the input signal. Before this positive feedback can begin, C202 must first discharge( sufficiently so asi to beY overcome by the input. Depending upon the =extent to which C202 was thus charged,vthe time to discharge sufficiently may be of Aa duration covering yone. or. more minority pulses which can therefore occur before the arnplifier is switched -back into, the preferred or majority state. Inasmuch as theV input signalpolarity favors the majority state, C202 need only discharge to the point where the input predominates. Once the charge on C202 reaches the state of equilibrium where it is of'comparable effectiveness with the input to cause switching to the non-preferred state, then theroutput will oscillate withthe number of pulses of one polarity being in a ratio with, the opposite polarity pulses according to the level of input signal.

The overall effect of this action ris seen tofbe the fde. velopment of a voltageon C202 which is related-to input signal amplitude. This capacitor voltage -is filtered by network R215, C203 and R210. The network output is a DLC. level having a Vpolarity and magnitude .of the input signal. Thus, the circuit of FIGURE 5 effects a linear amplification of the/input signal.'

The linear response in FIGURES has many useswhere linear amplification is desired. Forfexarnple, the circuit.

maybe employed ias a preamplifier.- Thus` for. illustration, the linear output is used to supply an input to asimple transiently regenerative amplifier circuit, such as shown in FIGURE '1, the input being first-applied to R211.y The output of the combination,I which affords a high degree of sensitivity, is then raswitched stateY correspon ing to the polarity of the signal across R211.

Diode D203 isolates the Q202 collector circuit from the effect of current flow through ystorage, feedback capacitor C202, thus preventing undue interference .by C202 during regenerative enabling times. Y

Resistor R210 holds the anode of D20-3 `at a relatively low potential between enabling times so that when enablingl commences, the potentials applied to the regenerative am-k plifier do not immediately start conduction through D203. In this mannenthe amplifier starts to regenerate into a particular state before the amplifier is loadedby output current which wouldotherwise alter ther response of the amplifier.

By varying the value of R213, the amountof feedback to the base of Q202 is controlled. By `having avery low V'amount of feedback, a longer train' of majority pulses occursbefore the input is overcome by the feedback. As the minority train nextcomrnences, C202 discharges at-a certain rate to the Vpoint where :the yinput signal takes over again. The filteredoutput isof increased. amplitude, thereby thus reducing the out-of-phase feedback effecting increases the gain of the linear amplifier; Conversely, increasing the yamount of feedback reduces the effective gain, inasmuch as the greater fthe feedback, the larger the tendency of the circuit to produce equaLnumbers of majority and minority pulses.

If the negative'fee-dback time constantzis substantially reduced so as to be relatively fast,- examination will show thatthe circuit'of FIGURES is transformed into a null oscillator. l

The circuit of FIGURE 6 is a phase-sensitive signal detector employing in-phase feedback. Thiscircuit includes a powersupply, a regenerative amplifier, an output rel-ay. energizing circuit, a response varying feedback; circuit and control means acting onthe feedback circuit .to render modifying feedback effective during Ialternate regenerative periods.

An input signalzisl supplied to regenerative amplifier circuit includes a shunting transistor Q303 which operates to shunt a feedback storage capacitor C301 every other half cycle of power supply operation. Consequently, the input is heavily latched during one regenerative period and substantially re-sensitized during the next period, this occurring in regular alternation.

The power supply comprises T301 with rectifiers D301 and D302 connected in full-Wave configuration thereto; the center tap of T301 is connected to the V+ positive bus, and the anodes of D301, D302 are connected together and tied to the negative bus, V-. The power supply output across V--, V+ consists of unfiltered pulsating D.C. having a frequency twice that of the power source at the primary of T301. The pulsating D.C. goes to a zero potential after each half-cycle.

Transiently regenerative amplifier Q301-Q302 is periodically enabled by the supply bus potential. The associated circuitry is in a balanced configuration.

A common emitter resistor R314 is connected from the V- bus to the connected emitters of Q301 and Q302A The collectors are returned through R305 Iand R300 respectively to the V+ bus. A double divider circuit across the rectifier output balances the nominal base potentials of Q301 and Q302. A first )branch comprises serially-connected resistors R303, R311 and a portion of potentiometer R312 to 'its tap, the latter being connected to V+; the second leg comprises R310, R313 and the remaining portion of R312 to its tap. The junction of R303 and R311 in the first branch is connected through R303 to the base of Q301; this junction is also connected to input terminal E302 and via R303 to the collector of Q302. The junction of R310 and R313 is coupled through R300 to the base of Q302. Input E301 is connected directly to the base of Q301.

The junction of R310 and R313 in the second divider is also coupled through R303 to the collector of Q301. The output of the regenerative amplifier is taken from the collector of Q302 and coupled via isolating diode D303 to the base Of Q304.

For producing output relay actuation, the potential applied to terminal E301 connected to the base of Q301 is negative with respect to the potential at terminal E302. A negative potential at the Q301 base tends to reduce Q301 base-emitter current when the enabling cycle commences. Consequently Q301 collector current is lower than it would be in a balanced condition, and the collector potential coupled through R303 and R303 to the base of Q302 is high. This potential causes increased base-emitter current in Q302 and therefore higher collector current therein. The resultant negative-going collector potential of Q302 is coupled through R303 and R303 back to the base of Q301. The negative-going potential reinforces the original negative input to the base of Q301, and consequently the Q301-Q302 circuit regenerates until Q302 is saturated and Q301 is cut-off. Regeneration occurs early in the power supply cycle and with only a very small potential on the Q301-Q302 collectors. The saturated state lasts until the end of the cycle, whereupon energizing potentials return to zero.

The Q301-Q302 output, for the negative-going input at E301, consists of the negative-going pulse at the Q302 collector. This negative-going output reduces the cathode potential of D303 sufficiently below that of its anode to start conduction. The D303 anode is coupled through R313 to V+, and also serially through D304 and R313 to the collector of relay output transistor Q303. Current through D303 flows in the base-emitter circuit of Q301 via R321 which is connected from the emitter of Q303 to V+. Resistor R320 connects the Q303 emitter to V-, maintaining the emitter below V+ so that Q303 is cut off when its base is effectively at the V+ potential, as when D303 is back biased.

With base-emitter current flowing, the Q303 collector current increases through the circuit of R323 and R322.

thus goes positive, base-emitter current flows, and current increases through the Q303 emitter-collector circuit comprising D303, the Q303, emitter-collector, and L301, all serially connected V- and V+. As a consequence, 'L301 is energized and produces the switched output corresponding to a negative input at E301.

When Q303 conducts, the potenti-al at its collector goes negative, and additional current flows through the baseemitter of Q301, also flowing through R303 `and D303. This provides a reinforcing effect whereby Q301 and Q305 are positively saturated.

For a positive input at' E301, Q301 and Q302 regenerate into the alternate state wherein Q302 is cut oif. The Q302 output is then positive, the cathode of D303 is biased positively with respect to its anode and is thus non-conducting. No energizing signal is impressed upon the Q303 base, and the L301 relay remains de-energized.

Diode D303 preferably has a relatively high level threshold. Thus, at the instant Q301-Q302 is first energized, D303 is non-conducting; this acts to isolated the Q302 collector from loading effects and allows regeneration into the appropriate state to occur uniiniuenced by the conditions of the output circuits.

The stored feedback circuit is connected from the collector of Q303 through network resistances R310 and R313 to E302. Feedback storage capacitor C301, paralleled by R315 and the collector-emitter circuit of Q303 in series, is connected between the junction of R313 and R313 and the emitters of Q301 and Q302. The base of Q303 is connected through R301 to V+, and through R302 to the cathode of power rectifier D302.

The potential at the collector of Q305 is attenuated by R313, stored in and delayed by C301, further attenuated by R317, and applied through R303 to input E301 (the base of Q301). For the assumed negative input at E301, this feedback is also negative, i.e., is in-phase with the input signal. For the illustrated response, the capacity of C301 is relatively large although the overall time constant is relatively short. The feedback network is designed to apply a large feedback potential to the base of Q301 when Q303 is non-conducting. Thus, a very large latching effect is obtained, requiring an extremely strong input sign-al to produce an .alternate state. This action occurs during alternate regenerative periods under control of shunting transistor Q303 which is non-conducting during half-cycles when its base is lheld positive by R301 and R302. During each next half-cycle, the base is madey negative, causing Q303 to conduct.

When Q303 is non-conducting, C301 stores a charge over an enabling cycle and thus has la relatively large charge on it at the beginning of the next enabling cycle, which charge provides the latching effect.

When Q303 conducts, the charge on C301 is dissipated except to the extent R315 preserves a residual small charge. This leaves a condition wherein the next regeneration of Q301 and Q302 finds a small amount latching at the Q301 base; this latching does not defeat the circuit sensitivity to low level inputs. In this manner, sensitive half-cycles alternate with latched cycles. Thus phase detection is attainable, the output polarity depending on the phase relation of the input signal and the regeneration switching signal. Also, the effect of spurious inputs synchronized with the power supply may be minimized. Thus, detect-ion of low level D.C. swamped by hum is facilitated and relay chattering minimized.

The foregoing embodiments are intended to be exemplary only. Other circuit configurations and applications will undoubtedly occur to those skilled in .the art. The invention is accordingly not limited to the specific mechanisms shown and described, but departures may be made therefrom within the scope of the accompanying claims without sacrificing its chief advantage or varying from the spirit thereof.

23 What is claimed is: l. A highly sensitive signal translating circuit comprising an amplifier including an input circuit for receiving an electrical parameter to be sensed, an output circuit for supplying a response indicative of said electrical parameter, and at least one stage between said input circuit and said output circuit; a positive feedback loop coupled to said amplifier for regeneratively driving the same into a saturated state related -to said electrical parameter when activated; a feedback control means coupled to said positive feedback loop for periodically activating andV impairing the regeneration of said feedback loop over successive time intervals short compared with said electricalv parameter;

signal storage means being coupled to said output circuit for storing a signal related to the saturated state of said amplifier; and

circuit means for coupling said signal storage means to the input of one stage in said amplifier to bias said amplifier in accordance with a saturated state resulting during a previous activation of said feedback circuit.

. 2. A circuit according to claim 1 further comprising a pulsating power supply for said amplifier and in which said feedback control means comprises said power supply.

3. A circuit according to claim 1 wherein said signal storage means and said coupling circuit means applyV a signal to said amplifier which is in-phase with the portion of said electrical paranietercausing said signal.

4. A circuit according to claim 1 wherein said signal storage means and said coupling circuit means apply a signal to said amplifier which is out-of-phase with the `portion of said electrical parameter causing said signal.

5. A highly sensitive signal translating circuit cornprising an amplifier including an input circuit for receiving an electrical parameter to be sensed,

an output circuit for supplying a response indicative of said electrical parameter, and

at least one stage between said input circuit and said output circuit;

a positive feedback lop coupled to said amplifier vfor regeneratively driving the sam-e into a saturated state relatedto said electrical parameter when activated;

a feedback control means coupled to said positive feedback loop for periodically activating and impairing the regeneration of said feedback loop over successive time intervals short compared with said electrical parameter;

a storage capacitor; and

a pair of resistors coupled between `the output of said output circuit and the input of one stage in said amplifier, said capacitor being connected to the junction between said resistors;

saidV capacitor and said resistors being so interconnected that said capacitor` stores a signal related to the saturated state of said amplifier and subsequently biases said amplifier in accordance with said stored signal.

6.- The circuitV accordang to claim 5 wherein said resistors are connected across an even number of amplifier stages.

7. The circuit according to claim 5 wherein-said resistorsV are connected across an odd number of amplifier stages.

8. A highly sensitive signal translating circuit comprising an amplifier including an input circuit for receiving an electrical parameter .to be sensed, an output circuit for supplying a response indicacircuit meansy coupling saidsignal storage means to the l input of one stage of said amplifier to bias said larnplifier in aiding relation'to saidelectrical parameter` if said parameter` remains the same during :successive activations of said l'positive feedback-loopu 9. A highly sensitive translating circuit in accordance with claim Sxwherein said feedback control means and said circuit means are isolated from said input circuit.

10. A highly sensitive translating circuitin accordance with claim 9 further comprising a pulsating power source andV wherein said pulsating power source is said feedback control means.

11..V The circuit according: to claim 8 wherein the combination 4of said storage means and coupling circuit means delays application of a signal :from said output circuit to said input of onestage for a period of time less than that between successive activations by said feedbackcomtrol means.y

12.. The circuit according to claim S wherein the Combination of said storage means and coupling circuit means delays application of a signal from said `'output circuit to said input of oneistage for a period of timesubstantially greater than that betweenpsuccessive activations by said feedback control means.

13. A highly sensitive signal translating circuit comprising an amplifier including an input circuit for receiving an -electrical paraml ete-r to be sensed, an output circuit for supplying a response indicative of said electrical parameter, and f at least oneamplifying. stagel between said input and output circuits; a positive .feedback loop coupled to saidy amplifier for regener-atively driving the same into a saturated state related to said electrical parameter when activated; a feedback control means coupled to said posi-tive feedback loop for periodicallyactivating. andimpairing the `regenerationcfsaid.V loop over successivewtime intervals short compared with said electrical parameter;

signal storage means connected to said output circuit for lstoring a signal related to said electrical parameter; and

circuit means couplingy said signal storage means to the'.

input of one stage of saidamplifier to bias said arnplifier in opposing relation tofsaid electrical parameter if said parameter remains the same during successive activations of said positive feedback loop.

14. A highly sensitive translating circuit in accordance Y with claim 13 further comprising a pulsating power source 25 delays application of a signal from said output circuit to said input of one stage for a period of time substantially greater than that between successive activations by said feedback control means.

17 A highly sensitive signal translating circuit comprising an amplifier including an input circuit for receiving an electrical parameter to be sensed, and

a plurality of stages including an output stage for supplying a response indicative of said electrical parameter;

a positive feedback loop coupled to said amplifier for regeneratively driving the same into a saturated state related to said electrical parameter when activated;

feedback control means coupled to said positive feedback loop for periodically activating and impairing the regeneration of said feedback loop over successive time intervals short compared with said electrical parameter;

first and second signal storage means coupled to said output stage for storing a signal related to the saturated state of said amplifier;

first circuit means for coupling za signal from said first storage means to the input of one stage of said amplifier in aiding relation to the portion of said electrical parameter causing said signal, and

second circuit means for coupling =a signal from said second storage means to the input of one stage of said amplifier in opposing relation to the portion of said electrical parameter causing said signal.

18. The circuit according to claim 17 wherein the time delay provided by said first circuit means and first storage means for said aiding signal is different from the time delay provided by said second circuit means and second storage means for said opposing signal.

19. The circuit according to claim 18 wherein the time delay for said aiding signal is less than that between successive activations by said feedback control means and the time delay for said opposing signal is substantially greater than that between successive activations.

20. The circuit according to claim 18 wherein the time delay for said aiding signal is substantially greater than that between successive activations by said feedback control means and the time delay for said opposing signal is less than that between successive activations.

21. The circuit according to claim 18 wherein the magnitudes of the aiding and opposing signals are different.

22. The circuit according to claim 21 wherein said aiding signal is larger than said opposing signal.

23. The circuit according to claim 21 wherein said opposing signal is larger than said aiding signal.

24. The circuit according to claim 18 wherein said aiding signal is 4applied during the operating cycle of said feedback control means and wherein said opposing signal is of a larger magnitude and applied lafter a time delay greater than said interval.

25. A highly sensitive signal translating circuit comprising an amplifier including an input circuit for receiving an electrical parameter to be sensed, and

an output circuit for supplying a response indicative of said electrical parameter;

positive feedback means included in said amplifier for driving said amplifier into a saturated state related to said electrical parameter when activated;

a pulsating source of power coupled to said amplifier and feedback circuit for Iperiodically activating said positive feedback circuit and said amplifier so that said electrical parameter is incrementally sensed during successive activations, and

the saturated state of said amplifier resulting from successive activations of said feedback circuit is 26 functionally related to said electrical parameter; signal storage means being connected to said output circuit for storing a signal related to the saturated state of said amplifier; and

circuit means for coupling said signal storage means to said amplifier to bias the same in accordance with the saturated state resulting during a previous activation of said feedback circuit.

26. A highly sensitive translating circuit in accordance with claim 25 wherein said pulsating source of power is an unfiltered full-wave power supply.

27. A circuit according to claim 25 in which said amplifier comprises a pair of transitor stages and wherein said positive feedback means comprises a common emitter interconnecting circuit.

28. A radiant energy responsive translating circuit comprising means providing an electrical parameter which varies in accordance with ambient radiant energy conditions;

an amplifier including an input circuit for receiving said electrical parameter to be sensed,

an output circuit for supplying a response indicative of said electrical parameter, and

`at least one stage between said input circuit and said output circuit;

a positive feedback loop coupled to said amplifier for regeneratively driving the same into a saturated state related to said electrical parameter when activated;

a feedback control means coupled to said positive feedback loop for periodically activating and impairing the regeneration of said feedback loop over successive time intervals short compared with said electrical parameter;

signal storage means being coupled to said output circuit for storing a signal related to the saturated state of said amplifier; and

circuit means for coupling said signal storage means to the input of one stage in said amplifier to bias said amplifier in accordance with a saturated state .resulting during a previous activation of said feedback circuit.

29. A temperature responsive translating circuit cornprising means providing an electrical parameter which varies in accordance with ambient thermal energy conditions;

an amplifier including an input circuit for receiving said electrical parameter to be sensed,

an output circuit for supplying a response indicative of said electrical parameter, and

at least one stage between said input circuit and said output circuit;

a positive feedback loop coupled to said amplifier for regeneratively driving the same into a saturated state related to said electrical parameter when activated;

a feedback control means coupled to said positive feedback loop for periodically activating and impairing the regeneration of said feedback loop over successive time intervals short compared with said electrical parameter;

signal storage means being coupled to said output circuit for storing a signal related to the saturated state of said amplifier; and

circuit means for coupling said signal storage means to the input of one stage in said amplifier to bias said amplifier in accordance with a saturated state resulting during a previous activation of said feedback circuit.

30. A highly sensitive signal translating circuit cornprising an amplifier including au input circuit for receiving an electrical parameter to be sensed,

an output circuit for supplying a response indicative of said electrical parameter, and at least one stage between said input circuit and said output circuit;

a positive feedback loop coupled to said amplier forV signal storage means including a `capacitor being cou pied to said output circuit for storing a signal'related to the saturated state of said amplier;

circuit means for coupling said signalstorage means to the input of one stage in said amplifier to bias said amplifier in accordance with a saturated state resulting during a previous activation of. said feedback circuit; and Y shunt circuit means connected across said capacitor for periodically discharging said capacitor in' said signal storage means.

31. The circuit accordingto claimt) wherein said signal storage means. comprises a capacitor, and said shunt circuit means is a transistor connected across said capacitor and Erendered conductiveduring every other activationtby said feedback control means.

References Cited bythe Examiner UNITED STATES t PATENTS 2,828,450 3/1958 'Pinckaers 330--26 XR 2,986,707 5/1961 BIeCher S30- 112 X 3,005,915 10/196lk Whiter etal. 330;.26 X 3,011,129 l11961 YMagleby et al. 328-73r X 3,106,684 10/1963 Luik S30-112 Xk 3,182,268 5/1965 Burwen 33'0-16 X RGY LAKE, Primary "Icczmz'ner,

R. P. KANANEN, yAssistant Examiner. f 

1. A HIGHLY SENSITIVE SIGNAL TRANSLATING CIRCUIT COMPRISING AN AMPLIFIER INCLUDING AN IN PUT CIRCUIT FOR RECEIVING AN ELECTRICAL PARAMETER TO BE SENSED, AN OUTPUT CIRCUIT FOR SUPPLYING A RESPONSE INDICATIVE OF SAID ELECTRICAL PARAMETER, AND AT LEAST ONE STAGE BETWEEN SAID INPUT CIRCUIT AND SAID OUTPUT CIRCUIT; A POSITIVE FEEDBACK LOOP COUPLED TO SAID AMPLIFIER FOR REGENERATIVELY DRIVING THE SAME INTO A SATURATED STATE RELATED TO SAID ELECTRICAL PARAMETER WHEN ACTIVATED; A FEEDBACK CONTROL MEANS COUPLED TO SAID POSITIVE FEEDBACK LOOP FOR PERIODICALLY ACTIVATING AND IMPAIRING THE REGENERATION OF SAID FEEDBACK LOOP OVER SUCCESSIVE TIME INTERVALS SHORT COMPARED WITH SAID ELECTRICAL PARAMETER; 